function t=qiugen(x0,y0,z0,m,n,p,f,c) 
A=m^2+n^2;
B=2*m*x0+2*n*y0-2*f*p;
C=x0^2+y0^2-2*f*z0-2*f*c;
t=[(-B+(B^2-4*A*C)^0.5)/(2*A)   (-B-(B^2-4*A*C)^0.5)/(2*A)];
